Agricultural experts are scrambling to quell fears of a global shortage of avocados following last week's Californian wildfires which burnt a path through the heart of American growing territory.

Initial reports suggested up to 20,000 acres of avocado trees in the San Diego region were destroyed, as much as a third of the Californian crop, which accounts for the vast majority of US avocados.

The Californian Avocado Commission believes this is an exaggeration and predicted this year's harvest would be 10% less than last year's of 166,000 tonnes.

"We'll know more in the coming weeks," said Guy Witney, director of industry affairs. "The commission will issue an updated crop estimate once all the information is in."

Avocados have become hugely popular over the last two decades, both eaten fresh and in processed form as guacamole. In Britain, consumption rose from 14,000 tonnes in 1990 to 30,000 tonnes in 2004.

Industry watchers assured British avocado connoisseurs there was no need to panic. The bulk of Europe's avocados are imported from Mexico, Chile or South Africa, with a minority from California.

Tommy Leighton, editor of the London-based industry publication Freshinfo, said the impact on British supplies was likely to be modest: "There's a large and growing avocado market in this country but it doesn't depend on California. The knock-on effect might be if stocks from other countries are diverted to America."

For Californian farmers, the setback comes soon after a water shortage and a rare February frost this year, which wreaked havoc in the state's citrus groves. Charley Wolk, a San Diego county farmer who grows avocados, citrus fruit and flowers, told local reporters: "It's not pretty. The freeze, the fire, the wind, and we're expecting a 30% water cut because of the drought." More than half of California's avocado farmers have no crop insurance and will face financial hardship.